Atlas of Anatomy

1 Bones, Ligaments & Joints

Vertebral Column: Overview

images The vertebral column (spine) is divided into four regions: the cervical, thoracic, lumbar, and sacral spines. Both the cervical and lumbar spines demonstrate lordosis (inward curvature); the thoracic and sacral spines demonstrate kyphosis (outward curvature).

Fig. 1.1   Vertebral column
Left lateral view.

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Spinal development

The characteristic curvatures of the adult spine appear over the course of postnatal development, being only partially present in a newborn. The newborn has a “kyphotic” spinal curvature (A); lumbar lordosis develops later and becomes stable at puberty (C).

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Fig. 1.2   Normal anatomical position of the spine
Left lateral view.

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Vertebral Column: Elements

Fig. 1.3   Bones of the vertebral column

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Fig. 1.4   Palpable spinous processes as landmarks
Posterior view. The easily palpated spinous processes provide important landmarks during physical examination.

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Fig. 1.5   Structural elements of a vertebra
Left posterosuperior view. With the exception of the atlas (C1) and axis (C2), all vertebrae consist of the same structural elements.

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Fig. 1.6   Typical vertebrae
Superior view.

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Cervical Vertebrae

images The seven vertebrae of the cervical spine differ most conspicuously from the common vertebral morphology. They are specialized to bear the weight of the head and allow the neck to move in all directions. C1 and C2 are known as the atlas and axis, respectively. C7 is called the vertebra prominens for its long, palpable spinous process.

Fig. 1.7   Cervical spine
Left lateral view.

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Fig. 1.8   Atlas (C1)

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Fig. 1.9   Axis (C2)

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Fig. 1.10   Typical cervical vertebra (C4)

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Injuries in the cervical spine
The cervical spine is prone to hyperextension injuries, such as “whiplash,” which can occur when the head extends back much farther than it normally would. The most common injuries of the cervical spine are fractures of the dens of the axis, traumatic spondylolisthesis (ventral slippage of a vertebral body), and atlas fractures. Patient prognosis is largely dependent on the spinal level of the injuries (see p. 600).

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This patient hit the dashboard of his car while not wearing a seat belt. The resulting hyperextension caused the traumatic spondylolisthesis of C2 (axis) with fracture of the vertebral arch of C2, as well as tearing of the ligaments between C2 and C3. This injury is often referred to as “hangman's fracture.”

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Thoracic & Lumbar Vertebrae

Fig. 1.11   Thoracic spine
Left lateral view.

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Fig. 1.12   Typical thoracic vertebra (T6)

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Fig. 1.13   Lumbar spine
Left lateral view.

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Fig. 1.14   Typical lumbar vertebra (L4)

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Osteoporosis

The spine is the structure most affected by degenerative diseases of the skeleton, such as arthrosis and osteoporosis. In osteoporosis, more bone material gets reabsorbed than built up, resulting in a loss of bone mass. Symptoms include compression fractures and resulting back pain.

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Sacrum & Coccyx

images The sacrum is formed from five postnatally fused sacral vertebrae. The base of the sacrum articulates with the fifth lumbar vertebra, and the apex articulates with the coccyx, a series of three or four rudimentary vertebrae.

Fig. 1.15   Sacrum and coccyx

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Fig. 1.16   Sacrum
Superior view.

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Intervertebral Disks

Fig. 1.17   Intervertebral disk in the vertebral column
Sagittal section of T11–T12, left lateral view. The intervertebral disks occupy the spaces between vertebrae (intervertebral joints, see p. 14).

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Fig. 1.18   Structure of intervertebral disk
Anterosuperior view with the anterior half of the disk and the right half of the end plate removed. The intervertebral disk consists of an external fibrous ring (anulus fibrosus) and a gelatinous core (nucleus pulposus).

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Fig. 1.19   Relation of intervertebral disk to vertebral canal
Fourth lumbar vertebra, superior view.

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Fig. 1.20   Outer zone of the anulus fibrosus
Anterior view of L3–L4 with intervertebral disk.

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Disk herniation in the lumbar spine

As the stress resistance of the anulus fibrosus declines with age, the tissue of the nucleus pulposus may protrude through weak spots under loading. If the fibrous ring of the anulus ruptures completely, the herniated material may compress the contents of the intervertebral foramen (nerve roots and blood vessels). These patients often suffer from severe local back pain. Pain is also felt in the associated dermatome (see p. 600). When the motor part of the spinal nerve is affected, the muscles served by that spinal nerve will show weakening. It is an important diagnostic step to test the muscles innervated by a nerve from a certain spinal segment, as well as the sensitivity in the specific dermatome. Example: The first sacral nerve root innervates the gastrocnemius and soleus muscles; thus, standing or walking on toes can be affected (see p. 398).

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Posterior herniation (A, B) In the MRI, a conspicuously herniated disk at the level of L3–L4 protrudes posteriorly (transligamentous herniation). The dural sac is deeply indented at that level. *CSF (cerebrospinal fluid).

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Posterolateral herniation (C, D) A posterolateral herniation may compress the spinal nerve as it passes through the intervertebral foramen. If more medially positioned, the herniation may spare the nerve at that level, but impact nerves at inferior levels.

Joints of the Vertebral Column: Overview

Table 1.2 Joints of the vertebral column

Craniovertebral joints

 

1

Atlanto-occipital joints

Occiput–C1

2

Atlantoaxial joints

C1–C2

Joints of the vertebral bodies

 

3

Uncovertebral joints

C3–C7

4

Intervertebral joints

C1–S1

Joints of the vertebral arch

 

5

Zygapophyseal joints

C1–S1

Fig. 1.21   Joints of the vertebral column

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Fig. 1.22   Zygapophyseal (intervertebral facet) joints
The orientation of the zygapophyseal joints differs between the spinal regions, influencing the degree and direction of movement.

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Fig. 1.23   Uncovertebral joints
Anterior view. Uncovertebral joints form during childhood between the uncinate processes of C3–C6 and the vertebral bodies immediately superior. The joints may result from fissures in the cartilage of the disks that assume an articular character. If the fissures become complete tears, the risk of pulposus herniation is increased (see p. 13).

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Proximity of spinal nerve and vertebral artery to the uncinate process

The spinal nerve and vertebral artery pass through the intervertebral and transverse foramina, respectively. Bony outgrowths (osteophytes) resulting from uncovertebral arthrosis may compress both the nerve and the artery and can lead to chronic pain in the neck.

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Joints of the Vertebral Column: Craniovertebral Region

Fig. 1.24   Craniovertebral joints

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Fig. 1.25   Dissection of the craniovertebral joint ligaments
Posterior view.

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images The atlanto-occipital joints are the two articulations between the convex occipital condyles of the occipital bone and the slightly concave superior articular facets of the atlas (C1). The atlantoaxial joints are the two lateral and one medial articulations between the atlas (C1) and axis (C2).

Fig. 1.26   Ligaments of the craniovertebral joints

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Vertebral Ligaments: Overview & Cervical Spine

images The ligaments of the spinal column bind the vertebrae and enable the spine to withstand high mechanical loads and shearing stresses and limit the range of motion. The ligaments are subdivided into vertebral body ligaments and vertebral arch ligaments.

Fig. 1.27   Vertebral ligaments
Viewed obliquely from the left posterior view.

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Table 1.3 Vertebral ligaments

Ligament

Location

Vertebral body ligaments

A

Anterior longitudinal ligament

Along anterior surface of vertebral body

P

Posterior longitudinal ligament

Along posterior surface of vertebral body

Vertebral arch ligaments

1

Ligamenta flava

Between laminae

2

Interspinous ligaments

Between spinous process

3

Supraspinous ligaments

Along posterior ridge of spinous processes

4

Intertransverse ligaments

Between transverse processes

Nuchal ligament*

Between external occipital protuberance and spinous process of C7

*Corresponds to a supraspinous ligament that is broadened superiorly.

Fig. 1.28   Anterior longitudinal ligament
Anterior longitudinal ligament. Anterior view with base of skull removed.

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Fig. 1.29   Posterior longitudinal ligament
Posterior view with vertebral canal windowed and spinal cord removed. The tectorial membrane is a broadened expansion of the posterior longitudinal ligament.

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Fig. 1.30   Ligaments of the cervical spine

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Vertebral Ligaments: Thoracolumbar Spine

Fig. 1.31   Ligaments of the vertebral column: Thoracolumbar junction
Left lateral view of T11–L3, with T11–T12 sectioned in the midsagittal plane.

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Fig. 1.32   Anterior longitudinal ligament
Anterior view of L3–L5.

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Fig. 1.33   Ligamentum flavum and intertransverse ligament
Anterior view of opened vertebral canal at level of L2–L5,Removed: L2–L4 vertebral bodies.

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Fig. 1.34   Posterior longitudinal ligament
Posterior view of opened vertebral canal at level of L2–L5. Removed: L2–L4 vertebral arches at pedicular level.

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